The invention lies in the field of medical engineering and concerns a method for fastening an implant to human or animal bone tissue as well as a corresponding implant system, wherein the implant may be designed e.g. as a replacement for the articulating surface of a joint, as a replacement for a larger bone section or another tissue or as an element for stabilizing a bone e.g. damaged by fracture. The invention further concerns a kit for carrying out the method.
Replacements of articulating surfaces of human joints are known, in particular, in connection with the tibia plateau in the knee joint (articulating surface with concave and convex portions), the glenoid cavity on the shoulder-blade and the acetabulum on the pelvis (concave articulating surfaces), but are also used for articulating surfaces of other joints (elbows, wrists, ankles or digital joints), in particular also convex articulating surfaces such as e.g. the articulating surface of the femoral head.
Known implants replacing articulating surfaces of joints (resurfacing implants) are flattish elements having a thickness which is smaller than their dimensions parallel to the bone surface and a concave and/or convex form and they usually comprise an essentially centered shaft or comb facing the bone tissue. These implants consist e.g. of a metal (e.g. titanium, titanium alloys or CoCr cast alloys) and carry on their side, facing the joint a bearing element, constituting the actual articulating surface and usually consisting of a synthetic material (e.g. polyethylene, in particular UHMWPE or ultra high molecular weight polyethylene). According to the state of the art, the implant is secured in the cancellous bone tissue of the appropriately prepared bone by means of a bone cement, by means of inserting screws into the bone through corresponding bores in the implant and/or by means of the shaft or comb being malleted into a corresponding opening in the bone tissue to achieve a press fit. It is further suggested to secure resurfacing implants not in the bone tissue beneath the implant, but in the cortical bone next to the implant, e.g. by clamping or screwing.
All named methods for securing resurfacing implants suffer specific disadvantages. The use of bone cement does not allow significant osseointegration, which would be advantageous for a durable connection. Screws extending through the implant require through bores and these bores and, subsequently, the heads of the screws inserted therein constitute friction points on the joint side of the implant, which is particularly detrimental if the implant constitutes the articulating surface (without bearing element) and the bores therefore are part of the articulating surface. Such friction points may also reduce the lifespan of a bearing element if it is movable on the joint side of the implant, as is usually the case for tibia plateau implants. Although securement by press fit permits osseointegration, it gives only a limited primary stability and, thus, necessitates a prolonged period of rest for the repaired joint. The above mentioned lateral securing requires additional space and therefore cannot be applied universally.
The implants for the replacement of larger bone parts or other tissues mentioned above in addition to the resurfacing implants may e.g. replace a complete joint ball including the neck. Such implants usually comprise a lengthy shaft to be secured in the marrow space of a tubular bone, again with the aid of a cement or with the aid of a press fit. According to the state of the art, implants for supporting or stabilizing bones e.g. damaged by fracture are often plates or rods with through bores to be attached to the bone e.g. by means of screws. In many of these cases the same aforementioned disadvantages of the named fastening methods apply.